What Are Market Indices

When the news says "the market rose 1.5% today" — what exactly rose? Not every stock at once. Journalists are referring to an index: a summary measure that tracks the behaviour of a specific group of securities.

A market index is a numerical indicator that follows the change in value of a predefined basket of securities. You cannot buy an index directly — it is a measuring scale, not an instrument. But understanding what it shows is essential for anyone who follows markets or chooses investments.

Why Indices Exist

Thousands of stocks trade every day. Watching each one separately is not practical. An index solves a simple problem: it compresses information about a large market into one number.

Indices serve several purposes:

• They show the overall direction of a market. If the index rises, the collective value of the companies in it has generally risen. If it falls, the opposite.
• They serve as a benchmark for comparison. If your portfolio grew 5% while the relevant market index grew 12% over the same period, your portfolio underperformed the market.
• They form the basis for passive investing. ETFs and index funds aim to replicate the composition of an index, giving investors a straightforward way to "buy the market" as a whole.

How an Index Is Calculated

Different indices are calculated in different ways. Two common approaches:

Market-capitalisation weighting

Larger companies have a larger influence on the index. If Apple's share price rises, the effect on the index is much bigger than if a small company's price rises. This is how the S&P 500 works.

Price weighting

Companies with a higher share price have a larger influence regardless of their overall size. The Dow Jones Industrial Average uses this approach: 30 large US companies, weighted by share price rather than by market value. This is a less common method today.

Most modern indices use market-capitalisation weighting, which more accurately reflects how much each company actually represents in the overall market.

The S&P 500

The S&P 500 is the most widely followed stock index in the world. It tracks 500 of the largest US publicly listed companies, weighted by market capitalisation adjusted for the free-float share of stock in public circulation.

A few important details:

• The index spans many sectors: technology, healthcare, financials, consumer goods, and others.
• The top ten companies can account for 30–35% of the total index weight. A small number of very large companies have a disproportionate effect on the overall number.
• The index is reviewed quarterly. Companies that no longer meet the criteria are removed; new ones are added.

The S&P 500 is often treated as a barometer of the US economy, but it reflects only public companies, and primarily large ones. Small businesses, private companies, and the public sector are not represented.

Why this matters for Ukrainian investors. Most global ETFs accessible through international brokers either track the S&P 500 directly or are closely related to it. When you hear that "the US market fell," this index is almost always what is being referred to.

The PFTS Index

The PFTS Index is the main equity index of the Ukrainian market. It tracks the most liquid shares trading on the PFTS Stock Exchange, weighted by market capitalisation adjusted for free float.

Several characteristics are worth understanding:

• Narrow base. Unlike the S&P 500 with 500 companies, the PFTS Index covers a very small number of actively traded stocks. The depth of Ukraine's equity market remains limited.
• Bond-dominated market. As discussed in the stock exchange article, trading volumes on PFTS are currently dominated by government bonds (OVDPs) rather than equities. The PFTS Index as an equity measure therefore reflects a very narrow segment of overall market activity.
• Limited economic representation. Many large Ukrainian enterprises have no publicly listed shares at all, or are listed abroad rather than on PFTS.

The PFTS Index is a useful reference for anyone investing in Ukrainian equities, but it is not broad enough to summarise the health of the Ukrainian business sector the way the S&P 500 summarises the US large-cap market.

What an Index Shows — and What It Does Not

Indices provide a useful picture, but they have limitations that matter in practice.

What an index shows:

• The general direction of the market over a given period.
• Relative performance: whether your portfolio is ahead of or behind the market.
• Market structure: which sectors or companies are the largest.

What an index does not show:

• Dividends are not always included. A "total return" index includes dividends reinvested; a "price return" index does not. The two produce different numbers over time.
• Volatility within the index. While the index holds steady, individual stocks inside it may move sharply in different directions.
• Future performance. A decade of index growth does not guarantee further growth.
• Company quality. A company can be in the S&P 500 and still have serious problems. Inclusion is not a quality endorsement.

Indices as the Foundation for Investing

Index investing is built on a straightforward idea: instead of picking individual stocks, buy "the whole market" through a fund that replicates an index.

An S&P 500 ETF (such as SPY or VOO on US exchanges) gives an investor proportional exposure to 500 large US companies through a single trade. Rebalancing, additions, and removals happen automatically inside the fund.

For a beginner, the implication is clear: once you understand what an index is, you already understand how most "simple" investment options for beginners are structured.

Summary

A market index is a measuring tool, not the market itself. It compresses the behaviour of a large group of securities into a single number and helps you see the overall picture.

The S&P 500 tracks 500 of the largest US companies and serves as a global reference point. The PFTS Index follows the most liquid Ukrainian equities, but because the domestic equity market is narrow, it reflects only a small slice of the Ukrainian corporate sector.

The key practical value of indices for an investor: they provide a benchmark against which portfolio results can be compared, and they form the basis for passive investment through ETFs and index funds.